DESCRIPTION: The Family Smoking Prevention and Tobacco Control Act of 2009 (FSPTCA) constructs a new regime of regulation and governance for tobacco products in the United States. In addition to important regulatory authorities granted to the Food and Drug Administration (FDA) over tobacco products already marketed (such as authorities to restrict advertising and marketing), the FSPTCA also accords the FDA significant authority over new, revised or modified tobacco products that have not yet been marketed (Sections 910 and 911). These sections reflect an important pre-market review authority for the FDA, an authority that the Administration exercises in other regulatory arenas (drugs, medical devices) by virtue of other statutes. As it currently stands, however, tobacco product sponsors may evade the requirements of new product or modified risk tobacco product requirements by filing a substantial equivalence (SE) application under Section 910 (a) (2)-(3). The FSPTCA defines substantially equivalent as meaning with respect to the tobacco product being compared to the predicate tobacco product, that the Secretary by order has found that the tobacco product - (i) has the same characteristics as the predicate tobacco product; or (ii) has different characteristics and the information submitted contains information, including clinical data if deemed necessary by the Secretary, that demonstrates that it is not appropriate to regulate the product under this section because the product does not raise different questions of public health (123 Stat. 1807-1808). We propose a study aimed at establishing foundations for a regulatory science of substantial equivalence, with a view to (a) harnessing the science of product equivalence from other realms, (b) understanding the economics and incentives facing tobacco product sponsors when submitting an SE application versus another kind of application, (c) generating a body of research that can inform rigorous evaluation of product applications for SE and other new product types, and (d) generating a body of research that can inform and advance the study of tobacco product equivalence and similarity in other settings. We divide our proposal into three parts: (A) a proposed analysis of legislation, legislative history and scientific methods for analysis of equivalence in other FDA-regulated product arenas; (B) a proposed regimen of testing to establish a 'regulatory science of substantial equivalence in tobacco products regulation (C) a proposed mathematical model of application incentives and scientific research production, with simulations; and stemming from the first two.